Negative electrode active material and lithium secondary battery comprising same

Abstract

A negative electrode active material according to an embodiment of the present invention includes spherical natural graphite, wherein the value of expression 1 below is 0.11 to 0.32. <Expression 1> (A-B2) / A In expression 1, A represents the cumulative volume (ml / g) of mercury permeated into the spherical natural graphite in a mercury intrusion curve when the pressure is raised from 1.4x10-4 MPa to 400 MPa, and B represents the cumulative volume (ml / g) of mercury remaining in the spherical natural graphite in a mercury discharge curve when the pressure is reduced to 0.14 MPa after being raised.

Description

Negative active material and lithium secondary battery containing the same

[0001] The present invention relates to a negative electrode active material and a lithium secondary battery including the same.

[0002] As the market for electronic devices such as mobile phones, laptops, and PCs grows, the market for lithium secondary batteries, the power source for these devices, is also growing rapidly. Furthermore, growing concern for environmental issues is driving demand for eco-friendly vehicles like electric vehicles, leading to research into lithium secondary batteries that can meet a variety of applications.

[0003] Among the components that make up a lithium secondary battery, the negative active material stores lithium ions during charging and plays a crucial role in determining factors such as improved charging speed and battery capacity. Among negative active materials, carbon-based materials typically use natural graphite or artificial graphite.

[0004] Among these, natural graphite is highly price-competitive and possesses a higher capacity than synthetic graphite. However, natural graphite has significant irreversible reactions and, with continuous charging and discharging, its volume expands, reducing the lifespan of secondary batteries.

[0005] Accordingly, a new technology that can suppress the volume expansion of natural graphite is required.

[0006] According to one embodiment of the present invention, a negative electrode active material capable of minimizing volume expansion and a lithium secondary battery including the same can be provided.

[0007] The objectives of the present invention are not limited to the above-described scope. Those skilled in the art will have no difficulty understanding the additional objectives of the present invention from the overall content of this specification.

[0008] According to one embodiment of the present invention, a negative active material comprises spherical natural graphite, wherein the spherical natural graphite has a value of the following formula 1 of 0.11 to 0.32.

[0009] <Formula 1>

[0010] (A - B 2 ) / A

[0011] In the above equation 1, A is 1.4x10 -4 In the mercury intrusion curve when the pressure is increased from MPa to 400 MPa, B means the cumulative volume (㎖ / g) of mercury that has infiltrated into the spherical natural graphite, and B means the cumulative volume (㎖ / g) of mercury that remains in the spherical natural graphite in the mercury emission curve when the pressure is reduced to 0.14 MPa after the pressure increase.

[0012] In addition, in the negative active material, the spherical natural graphite may have a value of 0.100 to 0.140 in the following equation 2.

[0013] <Formula 2>

[0014] B - A

[0015] In addition, in the negative active material, the spherical natural graphite may have a value of Formula 3 below of 1.5 or more.

[0016] <Formula 3>

[0017] A × V

[0018] In the above equation 3, V means the total volume (cm3 / g) of the micropore volume and mesopore volume of spherical natural graphite calculated from the nitrogen adsorption isotherm.

[0019] Additionally, in the negative active material, the spherical natural graphite may not include a carbon coating layer on the surface.

[0020] In addition, in the above negative active material, the average particle diameter (D) of the spherical natural graphite 50 ) may be 16.0 to 21.0 μm.

[0021] In addition, in the above negative active material, the powder orientation (I) calculated from the X-ray diffraction pattern of the spherical natural graphite 110 / I 004 ) can be between 0.1 and 0.9.

[0022] A secondary battery according to another embodiment of the present invention comprises a negative electrode; a positive electrode; and an electrolyte, wherein the negative electrode comprises any one of the negative electrode active materials described above.

[0023] The negative active material according to the present invention can suppress volume expansion and side reactions with an electrolyte due to continuous charge and discharge, and a lithium secondary battery including the negative active material can have excellent life characteristics.

[0024] The various advantageous and beneficial effects of the present invention are not limited to the above-described contents, and will be more easily understood in the course of explaining specific embodiments of the present invention.

[0025] Figure 1 is a graph showing mercury intrusion curves and mercury extrution curves for negative active materials manufactured in each example and comparative example.

[0026] Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0027] In addition, the embodiments of the present invention are provided to more completely explain the present invention to a person having average knowledge in the relevant technical field.

[0028] In describing the embodiments of the present invention, if a detailed description of a known technology related to the present invention is judged to unnecessarily obscure the gist of the present invention, such detailed description will be omitted. In addition, the terms described below are terms defined in consideration of their functions in the present invention, and these may vary depending on the intention or custom of the user or operator. Therefore, the definitions should be made based on the contents throughout this specification. The terminology used in the detailed description is only for the purpose of describing the embodiments of the present invention and should in no way be limiting. Unless clearly defined otherwise, expressions in the singular form include plural meanings.

[0029] In this description, expressions such as "including" or "having" are intended to indicate certain features, numbers, steps, operations, elements, portions or combinations thereof, and should not be construed to exclude the presence or possibility of one or more other features, numbers, steps, operations, elements, portions or combinations thereof other than those described.

[0030] Unless otherwise specified in the specification of the present invention, the % unit means weight %.

[0031] Below, the present invention will be described in detail through each embodiment or example of the present invention. It should be noted that each embodiment or example described in this specification is not limited to a single embodiment or example, but may be combined with other embodiments or examples. Therefore, the citation of a claim in the patent claims is only an example of an embodiment, and the technical concept of the present invention should not be interpreted solely as a combination with the cited claim, and combinations with various claims also fall within the scope of the technical concept of the present invention.

[0032] According to one embodiment of the present invention, a negative active material is provided.

[0033] According to one embodiment of the present invention, a negative active material comprises spherical natural graphite, wherein the spherical natural graphite has a value of the following formula 1 of 0.11 to 0.32.

[0034] <Formula 1>

[0035] (A - B 2 ) / A

[0036] In the above equation 1, A is 1.4x10 -4 In the mercury intrusion curve when the pressure is increased from MPa to 400 MPa, B means the cumulative volume (㎖ / g) of mercury that has infiltrated into the spherical natural graphite, and B means the cumulative volume (㎖ / g) of mercury that remains in the spherical natural graphite in the mercury emission curve when the pressure is reduced to 0.14 MPa after the pressure increase.

[0037] Based on the Mercury Intrusion Porosimetry method for spherical natural graphite, a Hg intrusion curve and a Hg extrusion curve can be obtained. Specifically, the mercury intrusion curve is a curve having a value of the cumulative volume of mercury intruded into the spherical natural graphite according to the pressure when the pressure increases, and the mercury extrusion curve can be a curve having a value of the cumulative volume of mercury remaining in the spherical natural graphite according to the pressure when the pressure decreases. In two-dimensional graph form, the mercury intrusion curve and the mercury extrusion curve can be a curve having pressure (psia) on the x-axis and cumulative pore volume (equal to the cumulative mercury volume experimentally, ㎖ / g) on ​​the y-axis. Meanwhile, the mercury intrusion curve and the mercury extrusion curve based on the mercury pressurization method can be obtained using Autopore 9520 (manufactured by Micromeritics).

[0038] Below, 1.4x10 -4When the pressure is increased from 400 MPa to 400 MPa, the cumulative volume of mercury (A, ㎖ / g) that has penetrated into the spherical natural graphite is referred to as the mercury intrusion amount, and when the pressure is reduced from 400 MPa to 0.14 MPa, the cumulative volume of mercury (B, ㎖ / g) that remains in the spherical natural graphite is referred to as the mercury residual amount.

[0039] The value of the above formula 1 is 0.11 to 0.32, specifically 0.11 to 0.30, more specifically 0.11 to 0.25, even more specifically 0.13 to 0.25, and even more specifically 0.13 to 0.16. The value of the above formula 1 is an index representing the stress of natural graphite, and when the value of the above formula 1 satisfies the above-mentioned range, the stress of natural graphite is implemented in an appropriate range, so that the particle expansion of natural graphite due to continuous charge and discharge can be minimized. In addition, when the value of the above formula 1 satisfies the above range, the movement path of lithium ions and the softness of natural graphite can be appropriately implemented through the control of the pore size and pore volume of natural graphite, thereby reducing the electrode expansion rate of the negative electrode and improving the life characteristics of the secondary battery.

[0040] For example, the spherical natural graphite may have a mercury intrusion amount (A) of 0.40 ml / g or more, specifically 0.45 ml / g or more, more specifically 0.50 ml / g or more, and even more specifically 0.55 ml / g or more. As a non-limiting example, the mercury intrusion amount (A) of the spherical natural graphite may be 1.0 ml / g or less, 0.9 ml / g or less, or 0.8 ml / g or less. When the mercury intrusion amount (A) of the spherical natural graphite satisfies the above-described range, the volume of the pores of the graphite is implemented in an appropriate range, so that the output characteristics of the secondary battery and the efficiency of slurry production during the production of the negative electrode can be improved.

[0041] For example, the mercury residue (B) of the spherical natural graphite may be 0.55 to 0.90, specifically 0.60 to 0.75, and more specifically 0.65 to 0.72. When the mercury residue (B) of the spherical natural graphite satisfies the above-mentioned range, the volume of the pores of the graphite and / or the stress of the natural graphite may be implemented within an appropriate range, thereby improving the output characteristics and life characteristics of the secondary battery.

[0042] For example, the value of the following Equation 2 for spherical natural graphite may be 0.08 to 0.16, specifically 0.09 to 0.15, more specifically 0.10 to 0.14, and even more specifically 0.11 to 0.13. In the following Equation 2, A denotes the amount of mercury intrusion into the spherical natural graphite, as defined in Equation 1. B denotes the amount of mercury residue in the spherical natural graphite, as defined in Equation 1. When the value of the following Equation 2 satisfies the above-mentioned range, the volume of the pores of the graphite is implemented in an appropriate range, so that the life characteristics of the secondary battery and the efficiency of slurry production during the production of the negative electrode can be improved.

[0043] <Formula 2>

[0044] B - A

[0045] For example, the powder orientation (I) of spherical natural graphite 110 / I 004 ) may be 0.1 to 0.9, more specifically 0.1 to 0.7, and more specifically 0.15 to 0.5. Meanwhile, the powder orientation (I 004 / I 110 ) is the maximum intensity (I) of the (004) plane diffraction peak in the X-ray diffraction pattern of the negative active material. 004 ) at the (110) plane, the maximum intensity of the diffraction peak (I 110) means the value obtained by dividing by the Cu-Kα line. Here, in the X-ray diffraction pattern of spherical natural graphite, the (110) plane diffraction peak can be located in the range of 76.5° < 2θ < 78.5°, and the (004) plane diffraction peak can be located in the range of 53.5° < 2θ < 56.0°, where 2θ represents the diffraction angle.

[0046] For example, the sphericity of the spherical natural graphite may be 0.85 or greater, specifically 0.86 or greater, and more specifically 0.87 or greater. As a non-limiting example, the sphericity of the spherical natural graphite may be 0.95 or less, 0.93 or less, or 0.92 or less. When the sphericity of the spherical natural graphite satisfies the above-mentioned range, the planes forming the layers of the natural graphite may be oriented in various directions, thereby further improving the capacity and output characteristics, and improving the energy density of the electrode. Here, the sphericity is a numerical expression of the degree to which a particle is close to a sphere, and may mean a value obtained by dividing the perimeter of a circle having the same area as a particle projection shape by the actual perimeter of the particle projection shape through a flow-type particle analyzer. Meanwhile, the sphericity can be measured using an analyzer for obtaining an optical image (Fluid Imaging Technologies, Flowcam 8100) and analysis S / W (visual spreadsheet).

[0047] For example, the spherical natural graphite may be in the form of particles in which natural graphite fragments are formed into bonds, folds, and / or assemblies. Specifically, the particulate natural graphite may be natural graphite particles in which natural graphite fragments are formed into a cabbage shape and assembled, or are formed into randomly formed, folded, and / or assembled, or are formed into a composite form of a cabbage shape and a random shape. In this case, an example of a composite form may be a form in which the central region of the particle is randomly assembled and the surface region is formed into a cabbage shape.

[0048] In terms of manufacturing method, the spherical natural graphite may be a particle whose shape is adjusted by mechanical processing (mechanical force) based on shear force, by forming, folding, and / or assembling natural graphite fragments derived from natural graphite having an anisotropic shape, such as flakes, and may be multi-heat-treated as described below. In this case, the natural graphite fragments may be primary particles of natural graphite that are formed, folded, and / or assembled as units derived from natural graphite having an anisotropic shape, and may substantially be crystal particles of natural graphite.

[0049] For example, the tap density of the spherical natural graphite may be 1.10 g / cm3 or less, specifically 1.05 g / cm3 or less, and more specifically 1.0 g / cm3 or less or 0.97 g / cm3 or less. As a non-limiting example, the tap density of the spherical natural graphite may be 0.75 g / cm3 or more, 0.78 g / cm3 or more, 0.80 g / cm3 or more, or 0.85 g / cm3 or more. When the tap density of the spherical natural graphite satisfies the above-mentioned range, the volume expansion rate of the electrode during charge and discharge can be suppressed, thereby improving the initial efficiency and / or life characteristics of the negative electrode active material. Meanwhile, the tap density can be measured as the packing density after tapping the natural graphite based on ASTM B527.

[0050] For example, the average particle diameter (D) of spherical natural graphite 50 ) may be 16.0 to 21.0 ㎛, specifically 16.3 to 20.8 ㎛, and more specifically 16.5 to 20.5 ㎛. The average particle diameter (D of the spherical natural graphite 50 ) If the above-mentioned range is satisfied, the adhesive strength of the electrode and the input / output characteristics of the negative electrode active material can be improved. Here, D 50 In the particle size distribution curve, it can mean the particle size (average particle size) at the 50% point of the volume accumulation. Meanwhile, D 50can be measured using a laser diffraction method. In one embodiment of the present invention, after the powder to be measured is dispersed in a dispersion medium, it is introduced into a laser diffraction particle size measuring device, and when the particles pass through a laser beam, the difference in diffraction pattern according to the particle size is measured, thereby calculating the particle size distribution.

[0051] Here, “D n " means particle size distribution, and can mean the particle size at the n% point of the volume accumulation amount in the particle size distribution curve. For example, D 50 is the particle diameter (average particle diameter) at the 50% point of the volume accumulation, and D 90 is the particle diameter at 90% of the volume accumulation, and D 10 is the particle diameter at the 10% point of the volume accumulation. Meanwhile, the particle size distribution can be measured using the laser diffraction method. Specifically, after the powder to be measured is dispersed in a dispersion medium, it is introduced into a laser diffraction particle size measuring device, and when the particles pass through the laser beam, the difference in diffraction pattern according to particle size is measured, thereby calculating the particle size distribution.

[0052] For example, the spherical natural graphite may have a specific surface area, specifically a BET specific surface area, of 4.50 m2 / g or more, specifically 4.80 m2 / g or more, more specifically 4.90 m2 / g or more, and even more specifically 5.00 m2 / g or more. As a non-limiting example, the specific surface area of ​​the spherical natural graphite may be 8.5 m2 / g or less, 8.0 m2 / g or less, 7.5 m2 / g or less, 7.0 m2 / g or less, 6.5 m2 / g or less, or 6.00 m2 / g or less. When the specific surface area of ​​the spherical natural graphite satisfies the above-described range, the volume expansion rate of the electrode during charge and discharge can be suppressed, thereby improving the initial efficiency and / or cycle life characteristics of the negative electrode active material.

[0053] For example, the spherical natural graphite may have a value of Equation 3 below of 1.0 or more, specifically 1.3 or more, and more specifically 1.5 or more. As a non-limiting example, the value of Equation 3 below of the spherical natural graphite may be 3.0 or less, 2.5 or less, or 2.0 or less. When the value of Equation 3 below of the spherical natural graphite satisfies the above-mentioned range, the movement path of lithium ions and the softness of the natural graphite can be appropriately implemented by controlling the degree of distribution of the pores of the graphite and the total volume of the pores, and accordingly, the life characteristics of the secondary battery, the efficiency of slurry production during the production of the negative electrode, and the electrode expansion rate of the negative electrode can be improved.

[0054] <Formula 3>

[0055] A × V

[0056] In the above equation 3, A is 1.4x10, the same as defined in equation 1. -4 In the mercury intrusion curve when the pressure is increased from MPa to 400 MPa, V means the cumulative volume (㎖ / g) of mercury that has infiltrated into the spherical natural graphite, and V means the total volume (㎤ / g) of the sum of the volume of micropores and the volume of mesopores of the spherical natural graphite calculated from the nitrogen adsorption isotherm. Specifically, the total volume (㎤ / g) can be the sum of the volume of micropores (㎤ / g) using the t-plot in the nitrogen adsorption isotherm of the spherical natural graphite and the volume of mesopores (㎤ / g) using the BJH (Barrett-Joyner-Halenda) method.

[0057] For example, spherical natural graphite may not include a carbon coating layer on its surface. Without a carbon coating layer, the volume expansion rate of the electrode during charge / discharge can be suppressed, and the capacity, initial efficiency, and lifespan characteristics of the negative active material can be secured.

[0058] According to another embodiment of the present invention, a method for producing a negative electrode active material comprising the above-described spherical natural graphite is provided.

[0059] A method for manufacturing a negative electrode active material including spherical natural graphite according to one embodiment of the present invention includes a multi-stage heat treatment step of heat-treating natural graphite, which has been shaped by mechanical force, at two or more different temperatures.

[0060] In detail, the multi-stage heat treatment includes a step of first heat treating natural graphite, which has been shaped by mechanical force, at a first heat treatment temperature of 500 to 1300°C in an inert atmosphere for 4 to 6 hours; and a step of second heat treating the natural graphite, which has been first heat treated in an inert atmosphere, at a second heat treatment temperature that is 50 to 200°C lower than the first heat treatment temperature, for 4 to 6 hours.

[0061] If necessary, the method for manufacturing a negative active material may further include a step (spheroidization step) of manufacturing spheroidized natural graphite having a spheroidization degree of 0.85 or more by mechanically processing natural graphite (raw material) having an anisotropic shape before the first heat treatment step.

[0062] For example, spheroidized natural graphite may be a material obtained by performing spheroidization once on spheroidized graphite. In this case, spheroidized graphite is graphite having an anisotropic shape, and the natural graphite obtained by performing spheroidization once on spheroidized graphite may have a shape with reduced anisotropy. The shape with reduced anisotropy may be a shape in which the sizes (lengths) in the three axes (l, m, n) directions are similar based on three mutually orthogonal axes having the center of the particle as the origin. The similarity in the sizes in the three axes may mean that the ratio between the larger and smaller values ​​(e.g., lm / ll, ln / ll) when comparing the size in one axis direction (ll) with the sizes in the other two axes directions (lm, ln) satisfies 0.8 to 0.95. A representative example of a shape in which the sizes in the three axes directions are substantially similar is a spherical shape. In this case, ll, lm, and ln can be experimentally measured through image observation, including observation with a conventional scanning electron microscope.

[0063] For example, mechanical processing may utilize equipment capable of applying shock compression, friction and / or shear forces, and may utilize at least one selected from the group consisting of ACM (Air Classifying milling), Spheronizing milling, Grinding milling, mechanofusion milling, planetary milling, Hybridization milling, shape milling and high speed milling.

[0064] In the multi-stage heat treatment including the first and second heat treatments, the inert atmosphere may be an inert gas atmosphere such as nitrogen, argon, helium, neon, or a mixture thereof, but advantageously, the inert gas may be nitrogen. When nitrogen is used as the inert gas, the surface of natural graphite can be maintained in a stable state without oxidation.

[0065] By performing the first heat treatment and the second heat treatment at the above-mentioned temperature and time, the pore size and pore structure of natural graphite change depending on the heat treatment temperature, and the mercury intrusion amount (A), the mercury residual amount (B), and the volume (total volume) of micro and meso pores change together. For example, as the heat treatment temperature increases, the mercury intrusion amount (A) decreases more rapidly, the mercury residual amount (B) decreases more gradually compared to the mercury intrusion amount (A), and the volume of micro and meso pores may tend to increase. At this time, the opposite trend may be exhibited as the heat treatment temperature decreases. In one embodiment of the present invention, when the heat treatment temperature satisfies the above-mentioned range, the mercury intrusion amount (A) and the mercury residual amount (B) are appropriately controlled to satisfy the range of the above-mentioned Equation 1, and further, the range of the Equation 1 and the above-mentioned Equation 2. In addition, when the heat treatment temperature satisfies the above range, not only the mercury intrusion amount (A) and the mercury residual amount (B), but also the total volume can be controlled to satisfy the range of the above-mentioned equation 3.

[0066] According to another embodiment of the present invention, an anode for a lithium secondary battery is provided. The anode according to one embodiment of the present invention may include any one of the aforementioned anode active materials. Hereinafter, the anode according to one embodiment of the present invention will be described.

[0067] A negative electrode according to one embodiment of the present invention may more specifically include a negative electrode current collector; and a negative electrode active material layer positioned on the negative electrode current collector and including the above-described negative electrode active material.

[0068] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0069] The above negative electrode active material layer may optionally include a binder and / or a conductive material together with the negative electrode active material.

[0070] The binder improves adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the negative electrode active material layer.

[0071] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One type alone or a mixture of two or more types of these may be used. The conductive material may typically be included in an amount of 1 to 30 wt% based on the total weight of the negative electrode active material layer.

[0072] The negative electrode according to one embodiment of the present invention can be manufactured according to a conventional negative electrode manufacturing method, except that the negative electrode active material described above is used.

[0073] Specifically, the composition for forming a negative electrode active material layer, including the aforementioned negative electrode active material and optionally a binder, a conductive agent, and a solvent, can be applied onto a negative electrode current collector, followed by rolling and drying. At this time, the types and contents of the negative electrode active material, binder, and conductive agent are as described above.

[0074] The solvent may be a solvent generally used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the negative electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the negative electrode.

[0075] Alternatively, the negative electrode may be manufactured by casting the composition for forming the negative electrode active material layer on a separate support, then peeling the film from the support and laminating the resulting film on a negative electrode current collector.

[0076] According to another embodiment of the present invention, a lithium secondary battery is provided. The lithium secondary battery according to one embodiment of the present invention may include the aforementioned negative electrode. Hereinafter, a lithium secondary battery according to one embodiment of the present invention will be described.

[0077] A lithium secondary battery according to one embodiment of the present invention may more specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0078] The above cathode is as described above.

[0079] In addition, the lithium secondary battery may optionally further include a battery container that houses an electrode assembly of a positive electrode, a negative electrode, and a separator, and a sealing member that seals the battery container.

[0080] The above positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer may include a positive electrode active material.

[0081] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 ㎛, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0082] The positive electrode active material may be a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound). Specifically, one or more of a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used. A specific example thereof may be a compound represented by one of the following chemical formulas:

[0083] Li a A 1-b B b D2 (in the above formula, 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5); Li a E 1-b B b O 2-c D c (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE 2-b B b O 4-c D c (In the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b B c D α(In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Co b B c O 2-α T α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Co b B c O 2-α T2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B c D α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Mn b B c O 2-α T α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B c O 2-α T2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni b E c G d O2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn dGeO2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li a NiG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a MnG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3(0 ≤ f ≤ 2); Li (3-f) Fe2(PO4)3(0 ≤ f ≤ 2); and LiFePO4. In the above chemical formula, A is Ni, Co, Mn or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; T is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; I is Cr, V, Fe, Sc, Y or a combination thereof; J may be V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0084] Of course, it is also possible to use a compound having a coating layer on the surface of the compound or a mixture of the compound and a compound having a coating layer.

[0085] The above coating layer may include at least one coating element compound selected from the group consisting of an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. The compounds forming these coating layers may be amorphous or crystalline. The coating elements included in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer forming process may use any coating method as long as it can coat the compound with these elements by a method (e.g., spray coating, dipping, etc.) that does not adversely affect the physical properties of the positive electrode active material, and since this is well understood by those skilled in the art, a detailed description thereof will be omitted.

[0086] The above-described positive electrode active material layer may further include a binder and / or a conductive material together with the above-described positive electrode active material.

[0087] The binder improves adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof, but is not limited thereto. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0088] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One type alone or a mixture of two or more types among these may be used, but the present invention is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0089] The above anode can be manufactured according to a conventional anode manufacturing method.

[0090] Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, including a positive electrode active material and optionally a binder, a conductive agent, or a solvent, onto a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive agent are as described above.

[0091] The solvent may be a solvent generally used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0092] Alternatively, the positive electrode may be manufactured by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the resulting film on a positive electrode current collector by peeling it off from the support.

[0093] The above separator separates the positive and negative electrodes and provides a passage for lithium ions to move. Any separator commonly used as a separator in lithium secondary batteries can be used without any particular restrictions. In particular, a separator having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0094] The above electrolyte may include, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0095] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0096] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be excellent when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0097] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, lithium salts include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable to use the concentration of the lithium salt within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above-mentioned range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0098] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0099] For example, a lithium secondary battery may be placed within a battery case. The shape of the battery case may be at least one selected from the group consisting of a cylindrical shape using a can, a square shape, a pouch shape, and a coin shape. However, the shape of the battery case is not limited thereto, and may have various shapes used in the relevant industry.

[0100] The present invention includes a battery module in which the secondary battery described above is used as a unit cell, and a plurality of unit cells are connected in series and / or in parallel.

[0101] The present invention includes a battery pack including a plurality of the above-described battery modules.

[0102] The present invention encompasses devices powered by the aforementioned secondary batteries, battery modules, or battery packs. Representative examples of such devices include electronic and communication devices such as mobile phones, laptops, and PCs, as well as electric vehicles.

[0103] Hereinafter, the present invention will be described in detail through examples. However, it should be noted that the examples described below are intended only to illustrate and concretize the present invention and are not intended to limit the scope of the invention. This is because the scope of the invention is determined by the matters set forth in the patent claims and matters reasonably inferred therefrom.

[0104] (Example 1)

[0105] (1) Manufacturing of negative active material

[0106] (Preparation of natural graphite powder) Average particle diameter (D 50 ) prepared primary spherical natural graphite powder having a particle size of 19 μm.

[0107] (After heat treatment), the natural graphite powder was heat treated at 600°C for 5 hours under a nitrogen atmosphere, and then heat treated at 500°C for 5 hours to manufacture a negative electrode active material.

[0108] (2) Manufacturing of cathode

[0109] The above-mentioned negative active material, Super P conductive agent, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a mass ratio of 96:1:1.5:1.5, and then dispersed in deionized distilled water to prepare a negative active material slurry. The negative active material slurry was applied to a Cu-foil current collector, and then dried and rolled to prepare a negative electrode having an electrode density of 1.10±0.05 g / cm3.

[0110] (3) Manufacturing of lithium secondary batteries

[0111] A coin-type 2032 half-cell was manufactured using the above-mentioned cathode as a working electrode and metallic lithium as a counter electrode. At this time, a separator made of a porous polypropylene film was inserted between the working electrode and the counter electrode, and the electrolyte used was a 7:3 volume ratio mixed solution of diethyl carbonate (DEC) and ethylene carbonate (EC) in which 1 M concentration of LiPF6 was dissolved.

[0112] (Example 2)

[0113] In the (heat treatment) step of the method for manufacturing the negative active material of Example 1, a negative active material, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that heat treatment was performed at 700°C for 5 hours and then at 600°C for 5 hours.

[0114] (Example 3)

[0115] In the (heat treatment) step of the method for manufacturing the negative active material of Example 1, a negative active material, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the heat treatment temperature was 900°C for 5 hours and then 800°C for 5 hours.

[0116] (Example 4)

[0117] In the (heat treatment) step of the method for manufacturing the negative active material of Example 1, the negative active material, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1, except that the heat treatment temperature was 1200°C for 5 hours and then 1100°C for 5 hours.

[0118] (Comparative Example 1)

[0119] The raw material in Example 1, the primary spherical natural graphite powder (average particle diameter (D 50 ): 19㎛) was prepared as a negative electrode active material. Using the negative electrode active material, a negative electrode and a lithium secondary battery were manufactured in the same manner as in Example 1.

[0120] (Comparative Example 2)

[0121] (1) Manufacturing of negative active material

[0122] Primary spherical natural graphite powder having an average particle diameter (D50) of 19 μm was prepared. Thereafter, the natural graphite powder (100 parts by weight) and petroleum pitch (3 parts by weight) were mixed and heat-treated at 1200°C for 10 hours to produce a negative electrode active material.

[0123] (2) Manufacturing of cathode and lithium secondary battery

[0124] A negative electrode and a lithium secondary battery were manufactured using the negative electrode active material of Comparative Example 2 in the same manner as in Example 1.

[0125] (Comparative Example 3)

[0126] (1) Manufacturing of negative active material

[0127] Average particle diameter (D 50 ) was prepared as a primary spherical natural graphite powder having a particle size of 19 μm. The natural graphite powder was filled into a mold and then cold isostatic pressing was performed to manufacture the negative electrode active material of Comparative Example 3. At this time, the cold isostatic pressing conditions were a pressurization rate of 5 MPa / min, a pressure of 150 MPa, and an isostatic pressing time of 1 minute.

[0128] (2) Manufacturing of cathode and lithium secondary battery

[0129] A negative electrode and a lithium secondary battery were manufactured using the negative electrode active material of Comparative Example 3 in the same manner as in Example 1.

[0130] Experimental Example 1: Measurement of the properties of negative active materials

[0131] The properties of the negative active materials manufactured according to the examples and comparative examples were evaluated as follows, and the results are shown in Table 1 and Fig. 1.

[0132] (1) Measurement of mercury intrusion amount and mercury residual amount

[0133] The mercury intrusion curve under pressurization and the mercury release curve under depressurization were measured based on the mercury porosimeter measurement method using Autopore 9620 (manufactured by Micromeritics). Using the mercury intrusion curve, 1.4x10 -4 The cumulative volume of mercury (A) that penetrated was calculated when the pressure increased from 400 MPa to 400 MPa, and the cumulative volume of mercury remaining (B) was calculated when the pressure decreased from 400 MPa to 0.14 MPa using the mercury release curve.

[0134] Specifically, 0.4 g of negative active material powder was placed in a powder cell and pretreated by degassing for 30 minutes at room temperature and vacuum (2.67 Pa or less). Afterwards, based on ISO 15901-1:2016, 1.4x10 -4 After depressurizing to MPa, mercury was placed in the cell and the pressure was increased to 1.4x10 -4 After increasing the pressure from MPa to 400 MPa, it was reduced to 0.14 MPa again. At this time, the mercury intrusion amount (A) during the pressure increase was calculated, and the mercury residual amount (B) after the pressure increase was calculated. The surface tension (γ) of mercury was 485 dyne / cm, and the contact angle (ψ) was 130˚. Using the measured mercury intrusion amount (A) and mercury residual amount (B), the value of Equation 1 ((A - B) 2) / A) and the values ​​(B - A) of Equation 2 were calculated, respectively. A graph showing the mercury intrusion curve and mercury emission curve of each of the negative active materials manufactured in the examples and comparative examples is shown in Fig. 1.

[0135] (2) Measurement of total pore volume

[0136] 2 g of negative active material powder was placed in a dedicated cylinder, pretreated at 100°C for 1 hour, and the total pore volume (V) was measured using the nitrogen adsorption method. In detail, the total pore volume was calculated from the nitrogen adsorption isotherm based on ISO 15901-2. The mesopore volume (cm) was measured using the Barrett-Joyner-Halenda (BJH) method. 3 / g) and the volume of micropores (cm) was calculated using a t-plot. 3 / g) was calculated. The total pore volume (cm 3 / g) is the volume of mesopores (cm 3 / g) and the volume of micropores (cm 3 / g) was calculated by adding them together. Using the measured mercury intrusion amount (A) and the total pore volume (V), the value of Equation 3 (A × V) was calculated.

[0137] (3) Surface area measurement

[0138] 2 g of negative active material powder was placed in a dedicated cylinder, pretreated at 100°C for 1 hour, and then the specific surface area was measured using the nitrogen adsorption method. The nitrogen adsorption isotherm was obtained by adsorbing nitrogen gas at 77 K using a surface area measuring device (Micromeritics, ASAP2020). From the nitrogen adsorption isotherm, the BET (Bruanuer Emmett Teller) method was used to determine the BET specific surface area (m 2 / g) was produced.

[0139] (4) Grain size (D) 10 , D 50 , D 90 ) measurement

[0140] For the negative active material, the particle size (D) was determined using the laser diffraction method. 10 , D 50 , D 90 ) was derived. D 90 , D 50 and D 10 can be defined as the particle sizes corresponding to 90%, 50%, and 10% of the volume accumulation amount in the particle size distribution curve, respectively.

[0141] (5) Tap density measurement

[0142] Based on ASTM B527, 15 g of negative active material powder was placed in a 25 ml container and tapped at 3000 cycles @ 284 cycles / min to measure the packing density.

[0143] Distinction Mercury intrusion amount (㎖ / g) Mercury residual amount (㎖ / g) Value of equation 1 Value of equation 2 Total pore volume (㎤ / g) Value of equation 3 Specific surface area (㎡ / g) D 10 (㎛)D 50 (㎛)D 90 (㎛) Tap density (g / cm3) Example 10.6040.7180.1470.1140.0261.575.0311.6618.9230.290.91 Example 20.5740.7020.1420.1280.0281.615.1211.2218.6529.600.96 Example 30.5350.6600.1860.1250.0311.665.4311.1918.7130.490.98 Example 40.4790.6040.2380.1250.0432.065.4612.0219.3330.261.04Comparative Example 10.5850.7270.0970.1420.0251.464.9612.5719.2629.990.89Comparative Example 20.2740.3690.5030.0950.0050.142.4113.9920.2930.261.07Comparative Example 30.50.5770.3340.0770.0180.907.259.5214.5921.281.03

[0144] Referring to Table 1 and Figure 1, for Examples 1 to 4, the mercury intrusion amount (A, ㎖ / g), mercury residual amount (B, ㎖ / g), total pore volume (㎤ / g), specific surface area (㎡ / g), D 10 (㎛), D 50 (㎛), D 90 (㎛) and tap density (g / cm3) were 0.479 to 0.604 ㎖ / g, 0.604 to 0.718 ㎖ / g, 0.026 to 0.043 ㎤ / g, 5.03 to 5.46 ㎡ / g, 11.19 to 12.02 ㎛, 18.65 to 19.33 ㎛, 29.60 to 30.49 ㎛, and 0.91 to 1.04 g / cm3. In addition, in the case of Examples 1 to 4, the value of Formula 1 ((A - B 2 ) / A), the values ​​of Equation 2 (B - A) and Equation 3 (A × V) were 0.142 to 0.238, 0.114 to 0.128, and 1.57 to 2.06, respectively. Meanwhile, in the case of Comparative Example 1, which did not perform the heat treatment process, the values ​​of Equation 1 and Equation 3 were measured to be lower, and the mercury residual amount (B) and Equation 2 were measured to be higher than in Examples 1 to 4. In addition, in the case of Comparative Example 2, in which the process of forming a carbon coating layer was performed instead of the heat treatment process, and in the case of Comparative Example 3, in which the process of isotropic pressing was performed instead of the heat treatment process, the value of Equation 1 was measured to be higher, and the values ​​of Equation 2 and Equation 3 were measured to be lower than in Examples 1 to 4. Experimental Example 2: Evaluation of electrochemical characteristics of lithium secondary batteries

[0145] The electrochemical characteristics of lithium secondary batteries manufactured according to the examples and comparative examples were evaluated as follows, and the results are shown in Table 2.

[0146] (1) Measurement of electrode expansion rate

[0147] After measuring the thickness of the negative electrode manufactured according to the Examples and Comparative Examples, the lithium secondary batteries manufactured according to the Examples and Comparative Examples were aged at 25℃ for 30 hours and then a charge-discharge test was performed. To evaluate the expansion characteristics, the reference capacity was 360 mAh / g, and the battery was charged to 5 mV at a constant current of 0.5 C, then switched to a constant voltage and charged until the end current reached 0.005 C. After a rest time of 10 minutes after charging, the battery was discharged 30 times at a constant current of 0.5 C with the reference capacity of 360 mAh / g until the battery reached 1.2 V. Afterwards, the battery was charged again to 5 mV with a constant current of 0.5 C, then switched to a constant voltage and charged until the end current reached 0.005 C. The battery was then disassembled, the electrode was washed with a dimethyl carbonate (DMC) solvent for 5 minutes, and the electrode thickness was measured to calculate the electrode expansion ratio using the following mathematical formula.

[0148] <Mathematical formula>

[0149] Electrode expansion rate (%) = (Thickness of electrode disassembled after 30 cycles - Thickness of electrode before assembly) / (Thickness of electrode before assembly) × 100

[0150] (2) Measurement of initial discharge capacity and initial efficiency

[0151] The secondary battery was aged at 25°C for 30 hours and then subjected to a charge-discharge test. To evaluate the initial capacity, the battery was charged to 5 mV at a constant current of 0.1 C with a reference capacity of 500 mAh / g, and then switched to a constant voltage to continue charging until the end current reached 0.005 C. After a 10-minute rest period after charging, the battery was discharged to 1.0 V at a constant current of 0.1 C with a reference capacity of 500 mAh / g. At this time, the initial discharge capacity was measured, and the initial efficiency was measured as the percentage of the initial discharge capacity to the initial charge capacity.

[0152] Electrode expansion ratio (%) Initial discharge capacity (mAh / g) Initial efficiency (%) Example 1 24.2 368.49 3.7 Example 2 24.7 365.99 3.5 Example 3 25.0 365.79 3.4 Example 4 25.3 366.49 3.8

[0153] Referring to Table 2, in the case of Examples 1 to 4, the electrode expansion rate was measured to be lower than that of Comparative Example 1 with an electrode expansion rate of 26.1% and Comparative Example 2 with an electrode expansion rate of 27.9%. That is, in the case of Examples 1 to 4, it was found that the volume expansion of the electrode due to continuous charge and discharge was minimized because the value of Equation 1 was appropriately adjusted. In addition, in the case of Examples 1 to 4, the initial efficiency was measured to be higher than that of Comparative Example 1 with an initial efficiency of 92.1%, Comparative Example 2 with an initial efficiency of 92.6%, and Comparative Example 3 with an initial efficiency of 93.0%. That is, since the negative active materials of Examples 1 to 4 have appropriate physical properties, it was confirmed that the electrochemical characteristics of the secondary battery including them are excellent. The above examples are only one example, and the present invention is not limited thereto. Anything that has substantially the same configuration as the technical idea described in the claims of the present invention and achieves the same operational effect is included in the technical scope of the present invention.

Claims

1. Contains spherical natural graphite, The above spherical natural graphite is a negative electrode active material having a value of 0.11 to 0.32 in the following formula 1. <Formula 1> (A - B 2 ) / A (In the above equation 1, A is 1.4x10 -4 In the mercury intrusion curve when the pressure is increased from 400 MPa to 400 MPa, B means the cumulative volume (㎖ / g) of mercury that has infiltrated into the spherical natural graphite, and B means the cumulative volume (㎖ / g) of mercury that remains in the spherical natural graphite in the mercury emission curve when the pressure is reduced to 0.14 MPa after the pressure increase.

2. In paragraph 1, The above spherical natural graphite is a negative electrode active material having a value of 0.100 to 0.140 in the following formula 2. <Formula 2> B - A 3. In paragraph 1, The above spherical natural graphite is a negative electrode active material having a value of 1.5 or more in the following formula 3. <Formula 3> A × V (In the above equation 3, V means the total volume (cm3 / g) of the micropore volume and mesopore volume of the spherical natural graphite calculated from the nitrogen adsorption isotherm) 4. In paragraph 1, The above spherical natural graphite is a negative electrode active material that does not include a carbon coating layer on its surface.

5. In paragraph 1, The average particle diameter (D) of the above spherical natural graphite 50 ) is a negative electrode active material having a diameter of 16.0 to 21.0㎛.

6. In paragraph 1, The particle orientation (I) measured from the X-ray diffraction pattern of the above spherical natural graphite 110 / I 004 ) is a negative active material having a value of 0.1 to 0.

9.

7. Cathode; Bipolar; and Contains electrolytes, A lithium secondary battery, wherein the negative electrode comprises a negative electrode active material according to any one of claims 1 to 6.

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